Dilute alkali dispersible hot melt bookbinding adhesives



Patented Oct. 27, 1953 DILUTE ALKALI DISPERSIBLE HOT MELT BOOKBINDING ADHESIVES Paul Swithin Pinkney, Niagara Falls, N. Y., as-

signor to E. I. du Pont de Nemours & Company, Wilmington, DeL, a corporation of Delaware No Drawing. Application December 8, 1949, Serial No. 131,900

3 Claims.

This invention relates to improvements in the art .of binding books, catalogs, magazines and pamphlets with'polymeric, organic, hot-melt adhesives. More particularly it relates to hot-melt vinyl resin 'bookbinding adhesives formulated to render them easily dispersible in aqueous dilute alkali .solutions to permit waste paper disposal in a conventional manner.

In application Serial No. 593,099 filed May 10, 1945, and now abandoned, having a common assignee with this invention is described a novel process of binding the page edges of books, magazines and similar articles of manufacture with solvent-tree, hot-melt viny1 resin adhesive compositions which permits dispensing With the conventional step of stitching with cord or stapling associated with conventional glue binding. That hot-melt process has met with significant trade acceptance because of the permissible speed-up of the binding operations as a result of the quick setting of hot melt adhesives in comparison with the slow setting aqueous glues. Furthermore, a superior adhesively bound volume is obtained in comparison with the glue bound product reinforced with stitching or with crash which is subject to deterioration wih age and by mold, moisture and loss of plasticity. Significant economy accompanied the adoption of the new process as a result of the increased rate of output, elimination of stitching or stapling steps and reduction in storage space normally required because of conventional practice of providing interrupted schedules for setting up the glue. Setting up the lu is n resented y a pr c s s d beuse tmo phe c humi it co diti ns fluen the rate at which the water is lost iron; the

aqueous glue.

Although the hot melt process met with commercial success, the superior quality of the adhesives was detrimental in one particular respect indirectly affecting the economies of the process. The .boo kbinding operations involve considerable trimming and consequently scrap accumulation. It is not profitable to consume the scrap for its fuel value and therefore the trimmings are sold as scrap paper andeventually reused in some form of processed paper products. Scrap paper is graded according to established standards and priced accordingly. Scrap containing substantial foreign matter is saleable only :at lowprices.

Trimmings containin considerable viny1 resin adhesive are particularly objectionable as paper scrap because the adhesive is waterinsoluble and cann be dispers d by con en o me s use i do inkine op rations and p oces s ass iate ith a er manu a ur and co i n. The un ispe sed a h sive part c es, unless s ntially removed, lead to spots or blemishes inthe final paper product. These adhesive particles also clog the felting screens of the paper machine, thereby preventing proper felting of the pulp slurry and consequently cause holes in final paper sheet. Adhesive particles are further deposited on the hot cylinder drying rolls where their adhesiveness may be-suificiently great to cause tearing of the felted paper web as it passes over the drying rolls.

As more and more hot-melt bookbinding adhesive is used, greater tonnage of catalogs, telephone directories, magazines and pocketbooks having the synthetic plastic adhesive incorporated therein will find its way into the scrap market and subsequently into the paper mills. Therefore, disposal of adhesive contaminated waste paper presents a serious problem.

It is an object of this invention to modify the bookbinding polymeric organic hot melt adhesives to remedy the above mentioned conditions in reference to waste paper disposal by rendering the adhesive dispersible in aqueous dilute alkali solutions normally used in conventional processing of paper scrap. Another object is to modify the composition of the polymeric adhesive chemically to provide susceptibility to dispersion in aqueous dilute alkali solution. A further object is to bind the edges of pages of books, catalogs and the like without stitching or stapling using a vinyl acetate copolymer hot melt adhesive composition which is dispersible in aqueous dilute alkali. Stil1 another object is to provide a book, catalog or similar article adhesively bound, without reinforcement with stitching or staples, by means of a vinyl acetate copolymer adhesive composition applied in hot melt condition, said adhesives being durable and resistant to water but which may be dispersed in aqueous dilute alkali to facilitate use of paper trimmings contaminated therewith and volumes subsequently disposed of as scrap paper.

These objects are accomplished by means of a hot melt adhesive composition which consists .essentially of a copolymer of vinyl acetate and crotonicacid, preferably the polymerization product of to 98 parts vinyl acetate and 10 to 2 parts of crotonic acid that is dispersible in aqueous dilute alkali solution, and. chlorinated diphenyl. Adhesive compositions formulated with these viny1 acetate-.crotonic acid copolymers and chlor nated diphenyl will d posit an adh siv which has free carboxylic groups capable of salt formation with water soluble alkalies, such as sodium, potassium, and ammonium hydroxides, said salts promoting dispersibility and solubility in water.

In the preferred embodiment of this invention, the pages of a book, catalog or similar article are bound with a thermoplastic adhesive composition consisting essentially of a vinyl acetatecrotonic acid copolymer of the said proportions and to 2 parts of a chlorinated diphenyl having from 42% to 60% chlorine substitution for each part of copolymer. 'A minor portion of a conventional compatible plasticizer, not more than 10% of the adhesive composition, may be included in the composition for modification of flexibility. Chlorinated diphenyls alter the properties of the vinyl acetate-crotonic acid copolymers from a thermoplastic resinous material having a gradual softening point to a composite blend having a sharply defined melting range as measured by the ball and ring method, the hot melt composition above its melting point rapidly becoming very liquid and capable of wetting and being adsorbed by the paper edges destined to become the backbone of the book.

The following examples are given by way of illustration only and no limitations are intended thereby except as indicated in the appended claims.

Example 1 A mixture of 349.5 parts vinyl acetate, 10.5 parts crotonic acid, 620 parts tertiary butyl alcohol, and 3.5 parts of a polymerization initiator such as a,a'-aZO-bls (isobutyronitrile) described in U. S. Patent No. 2,471,959 was heated under reflux for two hours. The tertiary butyl alcohol and unreacted vinyl acetate were removed by steam distillation, leaving 212 parts of vinyl acetate/crotonic acid copolymer. The copolymer was dissolved in dilute ammonium hydroxide and precipitated by addition of hydrochloric acid. The copolymer thus precipitated was found, by titration, to contain 4.1% by weight of combined crotonic acid.

The above-mentioned copolymer was heat blended with chlorinated diphenyl (containing 54% chlorine), in a ratio of 12 parts of copolymer to 8 parts of chlorinated diphenyl. This mixture had a melt viscosity of 32.4 poises at 160 C. and was suitable for use as an adhesive.

Example 2 Chlorinated diphenyl (42% chlorine) was mixed with vinyl acetate-crotonic acid copolymer to give the following composition:

Per cent Chlorinated diphenyl 50.0 Vinyl acetate/crotonic acid copo1ymer 49.9 Inhibitor 0.1

The copolymer was estimated to consist of 93.6 parts vinyl acetate and 6.4 parts crotonic acid. The inhibitor used was Ionol which is a proprietary antioxidant sold on the open market and described as a trisubstituted or hindered phenol having a molecular weight of 220.3 and a melting point of 70 C.

This product, which can be used as a hot melt adhesive, was dispersible in dilute alkali and was thermally stable for at least '72 hours at 160 C. without loss of its dilute alkali dispersibility. By dilute aqueous alkali solutions is meant alkalinity of the order of 05% sodium hydroxide or its equivalent.

This hot melt adhesive, when used to bind books as described later, yielded an excellently bound volume having a tough, flexible backbone which was water-proof and resistant to deterioration with age and exposur to atmospheric conditions.

Example 3 The following composition was charged into an agitated polymerization kettle:

Parts by weight Toluene 124 Vinyl acetate 300 Crotonic acid 14 Polymerization initiator 0.9

A suitable initiator is azo-bis(isobutyronitrile).

This mixture was heated to 70 C. and as polymerization proceeded, the temperature rose to a plateau at about 91 C. Additional initiator (0.25 part) was charged into the kettle and polymerization continued until a plateau at about 98 C. was reached under moderate reflux. Onehalf part of Ionol was added to arrest the polymerization. Two hundred parts chlorinated diphenyl (54% Cl) were charged into the kettle and thoroughly mixed with the polymerized charge. The toluene and unpolymerized vinyl acetate were then removed by distillation under vacuum (50 mm.) until the temperature reached 160 C. In this way 176 parts of distillate was obtained, leaving about 460 parts of adhesive as residue.

The adhesive was calculated to have the following composition:

Per cent Chlorinated diphenyl 47.8 Vinyl acetate crotonic acid copo1ymer 52.1 Inhibitor 0.1

The copolymer was estimated to contain about 5.6' parts of crotonic acid and 94.4 parts vinyl acetate.

This hot melt adhesive was equivalent to that of Example 2, exhibiting heat stability for at least '72 hours at 160 C. without loss of its dispersibility in dilute alkali. Likewise applied in the art of binding books with hot melt adhesives, it yielded an acceptably bound volume having the characteristics desirable for durable bindings and in addition, the adhesive contaminated trimmings and scrap thereof had full salvage value because the adhesive was adequately removed by alkali dispersibility by the orthodox operations.

By further experimentation it has been found that similar hot melt adhesive compositions in which the copolymer contained as little as 2% crotonic acid exhibit adequate dilute alkali dispersibility. The preferred content of crotonic acid is in the range of 2 to 10%, the balance being vinyl acetate. Still higher contents of crotonic acid promote solubility in dilute alkali. However, higher contents of this monomer lead to low molecular weight copolymers and exceptionally long polymerization cycles. Th resultin low molecular weight copolymers are lacking in toughness, are soft and exhibit cold flow, properties which characterize the copolymer as inadequate for use in hot melt adhesives for binding books. Other fields of adhesive application may tolerate sacrifice in these properties and find utility for hot melt adhesives formulated with fcopolymer's having a higher content than of crotonic acid copolymeri'zed therein. For example, "such hot melts can be used for attachment of labels to glass and metal containers Wh'ere'itls desirableto subsequently remove the label by soaking in very dilute aqueous alkali solutions.

The foregoing examples show a two component hot-melt composition, that is, vinyl acetatecrotonic acid copolymer modified with chlorinated diphenyl as a liquefying softener. The products may be further modified with compatible orthodox ester plasticizers to alter the physical characteristics of the adhesive film. Generally the use of hot melt adhesives for the purpose of binding books limits the acceptable content of such plasticizers to 10% based on the total weight of non-volatile hot melt adhesive. D'i- (methyl cellosolve) phthalate and triethyl citrate are particularly useful for plasticizing the vinyl acetate-crotonic acid copolymer adhesive. .Iricresyl phosphate, dicresyl carbitol, butyl 'phthallyl butyl glycollate, ortho-cresyl paratoluene sulfonate and polyethylene glycol di-Z- ethyl hexoate may also be used. Use of the latter plasticizer is particularly disclosed in Example '1 of application Serial No. 593,099 filed 'May 10, 1945, and now abandoned. Although this plasticizer shows excellent compatibility with polyvinyl acetate, its compatibility with the vinyl acetate-crotonic acid copolymer is more limited and in some instances it may not be used to the full extent of 10%.

It is obvious that the adhesive used for binding pages without the reinforcing action of staples or stitched thread to form the backbone of the volume must 'be characterized by greater toughness, flexibility and freedom from cold flow than adhesives used .for other binding purposes, such as for attaching the cover to the said backbone. Consequently, for purposes of economy, the adhesive normally used in forming the backbone may be modified with low cost diluents when used as a cover adhesive. The following example is representative of a satisfactory cover adhesive which may be used either in combination with the hot melt bound backbone or alone to attach covers to stitched or stapled volumes.

Example 4 Vinyl acetate and crotonic acid were copolymerized in toluene and the liquefying softener added to displace the solvent as described below.

The following ingredients were charged into the polymerization kettle with stirring:

Parts by weight Toluene 124 Vinyl acetate 300 Crotonic acid '14 Polymerization initiator 0.9

Polymerization was carried outfor about '7 hours while the temperature increased from 70 .C. to 91 C. Then 0.25 part of additional polymerization initiator was charged into the kettle and the temperature increased from 91 C. to a'plateau at 97 C. in about five hours. At this temperature, the polymerization was arrested by addition of 0.5 part of inhibitor (Ionol). Two hundred twenty parts of chlorinated diphenyl having 54% chlorine substitution were charged into the hot copolymer solution and distillation was commenced under 50 mm. vacuum to displace the toluene and remove the excess vinyl acetate. Distillation'was stopped at 160C. at which-pointZOO 6 parts ofdmtillatehad collected. To the solvent free hot melt adhesive remaining in the kettle were added .145 parts of chlorinated diphenyl, 103.2 parts of Vinso1 resin, 141 parts of asbestine (a complex hydrated magnesium silicate of fibrous, crystalline structure) and 1.4 parts inhibitor (Ionol) for a final total charge of 841.1

parts.

The ultimate composition of the resulting hot This hot melt adhesive containing low cost diluents was found to be heat stable for about 72 hours at C. and adequately retained its dispersibility in dilute alkali. When used as an adhe'sive fora'ttaching covers, the product was found "to be entirely satisfactory for the purpose. The

use of the diluents, however, contributed brittleness and detracted from the toughness and flexibility inherent in the undiluted adhesive making it less desirable as a backbone adhesive.

Example 4 shows the use of resinous and mineral diluents. Still other diluents which are inert, non-volatile and heat stable for periods of 72 hours and longer in the presence of the hot melt composition at 160 C. may be used. Cotton flock, regenerated cellulose flake particles, glass fibers and the like, of which the maximum average dimensions are about 0.12 inch and the ratio between length and diameter or thickness is in the range of 20-100 to 1, may also be used as diluents. Embedded in the applied adhesive, theyexhibit reinforcing strength. Obviously due to matting effects, the amount of this diluent is limited. In the art of binding books and cover application, it is preferred that the content of this type of diluent does not exceed 7% based on the total adhesive composition.

The solvent used as a polymerization medium has an effect on the molecular weight of the polymer or copolymer. When tertiary butanol was used as solvent in place of toluene, a higher intrinsic viscosity product was obtained. However, in general, these copolymers have viscosities in they range of commercially low viscosity vinyl acetate polymers. The copolymerization can also be carried outin benzene or ethyl alcohol.

:The nature of the polymerization initiator also affects the molecular weight or" the copolymer.

Peroxide initiators, such as lauroyl peroxide and 'benzoyl peroxide, and azonitrile initiators, such as a,e'-azo-bis(isobutyronitrile) and a,a'aZ0blS- (alpha-gamma dimethyl valeronitrile) give copolymers having molecular weights which are satisfactory for hot melt adhesive and which are dispersible'indilute alkali. In general, any polymerization initiator which is satisfactory for the polymerization of vinyl acetate can be used for the copolymerization of vinyl acetateand crotonic acid.

The adhesives of the present invention may be used in the same manner as other hot melt adhesives in binding books. The basic design of a machine commercially used for binding books us ing glue is the bookbinding and covering machine described in the Bredenburg U. S. Patent No. 1,073,324. Numerous subsequent patents show modification in the machines and improved steps in the process of binding books involving such machines. Application Serial No. 593,099 filed May 10, 1945, describes modification of the process of binding books and similar articles by substitution of a solvent-free hot melt polyvinyl acetate adhesive composition for the glue and elimination of the steps of stitching or stapling to reinforce the glue binding. Briefly, in commercial practice, the folded signatures subsequently to become pages of the bound volume are assembled between fiat metal plates held together under pressure, the position of the gathered signatures being adjusted between the clamping plates to leave about to inch of page backbone edge exposed after the cutting operation has trimmed off the signature folds to reduce the signatures to a plurality of pages. The assembled clamped signatures are then passed through cutter to remove the said signature folds. ihe backbone now having a smooth uniform edge is subjected to roughers which serve the purpose of opening up the fibers at the edges of the pages to make them more receptive to the adhesive composition to provide better keying action by permitting the composition to penetrate into the interstices. Roughing may vary in degree and pattern to produce the desired keying action. The roughened edge is then freed of loose extraneous material by brushing, air-blast or vacuum means. Following these preparatory steps, the hot melt adhesive is applied to the backbone edge by means of a conventional applicator roll consisting of a fiat surfaced wheel revolving in and about immersed in a hot melt adhesive, such as described in Examples 1 and 2, maintained at a temperature of about 169 C. An adjustable scraper-"doctor blade or metering hot spinner removes the excess ad" hesive, leaving the desired thickness of film on the backbone. The adhesive application may be single stage or by multiple coats applied by subjecting the backbone to a series of adhesive ap' plicators.

The application of a priming coat may precede the application of the principal hot melt adhesive. The primer is generally identical with the solvent free, hot -elt adhesive except it is cut with a volatile solvent which reduces the viscous hot melt to a very thin, penetrating liquid. The use of the primer necessitates provision of adequate means of substantially removing the volatile component of the applied primer prior to application of the hot melt. Obviously, since dilute alkali dispersibility is the object of the invention, it is pertinent that the deposited primer, like the principal adhesive, be characterized by that property.

As an alternative to priming the backbone of the book with a solution type primer, an aqueous dispersion of polyvinyl acetate containing a small percentage of polyvinyl alcohol as the dispersing and stabilizing agent may be used as a primer. Apparently the polyvinyl alcohol promotes redispersibility of the deposited primer in aqueous media, although a hot-melt adhesive formulated with vinyl acetate polymer is inadequately dispersible in dilute aqueous alkali solutions.

While the applied hot melt adhesive film is still in a substantial fluid condition an open mesh fabric or crash may be embedded therein to reinforce the backbone if such strengthening of the volume is desired. Finally the cover is attached following application of any of the solvent-free hot melt, heat-stable, alkali dispersible adhesives described herein. Example 4 which contains economical diluents is representative of a solventfree hot melt adhesive entirely satisfactory for cover application. The covering machine may be separate from the main bookbinding machine which provides the means of converting the signatures to an uncovered volume having an adhesively bound backbone. Consequently, the covering operation using a hot melt adhesive may be employed in covering magazines, pocketbooks, pamphlets, catalogs, etc. in which the signatures are held together with staples or stitched cord with or without the presence of conventional adhesives.

The trimming operations in the process of binding books, magazines and the like result in waste paper scrap contaminated with adhesive. When this adhesive is a conventional proteinaceous glue, the disintegration processes used by the paper converters in consuming the scrap cause the glue to disperse or dissolve, thereby providing a means of separation of substantially all of the adhesive to the extent that the ultimate product is unaffected by the small content of adhesive that may have been retained. When the adhesive is an orthodox resinous or elastorneric composition formulated with water insoluble polymers, the paper manufacturer using the waste paper encounters difiiculty in using the scrap because the adhesive is not adequately and substantially dispersed and removed.

The waste paper and scrap contaminated with the adhesives of this invention formulated essentially with a copolymer consisting of the polymerization product or" to 98 parts vinyl acetate and 10 to 2 parts of crotonic acid and chlorinated diphenyl present no problem to the paper converter inasmuch as the adhesive is solubilized or dispersed in aqueous dilute alkali solution containing .05% sodium hydroxide. Dispersion in .01% caustic has been obtained by lengthening the contact time.

The trim or adhesive contaminated waste paper is generally consumed by paper mills in th manufacture of new paper. Mills which experienced serious difficulty in using waste paper contaminated with polyvinyl acetate to the extent that such type of scrap would not be purchased had no difficulty in using scrap contaminated with an equivalent adhesive in which the vinyl acetatecrotonic acid copolymer of this invention was substituted for polyvinyl acetate in the formulation.

A distinct advance in the art of bookbinding, particularly in the art of binding books, magazines, catalogs and the like with a solventfree, hot melt polymeric resinous adhesive has been made by the use of adhesives comprised essentially of a copolymer consisting of the polymerization product of 90 to 98 parts by weight or" vinyl acetate and l!) to 2 parts of crotonic acid and a chlorinated diphenyl, the latter being present preferably in the range of to 2 parts for each part of copolymer. The use of the said hot melt adhesives characterized by dispersibility or solubility in aqueous dilute alkali at concentrations as low as .01% NaOH equivalent, preferably about 05%, serves to eliminate a serious disposal prob- 1cm in reference to use of waste paper contaminated with hot melt polymeric adhesive which heretofore was not dispersible during conventional waste paper processing. These advantages were economically accomplished without sacrifice in desirable characteristics of the adhesive, such as toughness, flexibility and. freedom from cold flow.

As many apparently widely different embodiments of this invention may be made without de- 9 parting from the spirit and scope thereof, it is to be understood that the invention is not limited, to the specific illustrations given except as defined in the appended claims.

I claim:

1. A thermoplastic adhesive composition which is characterized by the retention of its thermoplastic properties after it has been heated to 60 C. for an extended period of time, which comprises one part of a copolymer of from 90 to 98 parts of vinyl acetate and 10 to 2 parts of crotonic acid, and from to 2 parts of a liquefying softener consisting essentially of a, chlorinated diphenyl.

2. The composition of claim 1 in which the chlorinated diphenyl contains from 42% to 60% chlorine.

3. The composition of claim 1 which contains a polymerization inhibitor.

PAUL SWI'I'HIN PINKNEY.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date Kirshbraun Feb. 14, 1928 Gale Aug. 18, 1931 Starck et a1. Nov. 25, 1941 Zahniser Mar. 24, 1942 Patnode May 12, 1942 Pollack Dec. 22, 1942 Widder et a1 Feb. 9, 1943 Humphrey May 11, 1943 Patton Oct. 2, 1945 Dean et a1 Dec. 11, 1945 Murphy et a1 Nov. 1, 1949 Curtis May 2, 1950 OTHER REFERENCES Monsanto Plasticizer, 1949, pages 27-28. 

1. A THERMOPLASTIC ADHERSIVE COMPOSITION WHICH IS CHARACTERIZED BY THE RETENTION OF ITS THERMOPLASTIC PROPERTIES AFTER IT HAS BEEN HEATED TO 160* C. FOR AN EXTENDED PERIOD OF TIME, WHICH COMPRISES ONE PART OF A COPOLYMER OF FROM 90 TO 98 PARTS OF VINYL ACETATE AND 10 TO 2 PARTS OF CROTONIC ACID, AND FROM 1/2 TO 2 PARTS OF LIQUEFYING SOFTENER CONSISTING ESSENTIALLY OF A CHLORINATED DIPHENYL. 